The aim is to determine how the action potential causes muscle contraction. Two sub-microscopic intracellular systems of vesicles and channels are important in linking the two events: the T-system and the sarcoplasmic reticulum. The voltage-clamp technique will be used to investigate electrical excitation in the T-system, as well as electrical signs of sarcoplasmic reticulum/T-system interaction. Experiments will be designed to study the extent to which the T-system is capable of regenerative changes in Na ion-permeability, and to assess the role of non-ionic gating currents in the regulation of contraction.